Modern society began to flourish only when humans figured out how to deliver reliable water supplies to larger and larger concentrations of people, and how to remove the accumulations of waste that cities produce, thus reducing outbreaks of water-related diseases. Those services, which most of us take for granted, are still pipe dreams for vast populations in the poorest places on the planet.This failure to meet the basic human need for water has direct, tangible and unacceptable consequences: drink dirty water and you get sick. Witness the father caring for his son afflicted by a guinea worm parasite. See the girl wasting away from cholera. Look at the consequences of arsenic poisoning on Bangladeshi villagers. And know that all of these diseases are completely preventable.More than half the population of our modern,"civilized"world still suffers from water services inferior to those of the ancient Greeks and Romans. As a result, water-related diseases continue to be a serious problem in many parts of the world.Water-related diseases fall into several types or classes, but the three that are most clearly associated with the failure to provide safe water and sanitation are waterborne, water-washed and water-based diseases.Waterborne diseases include those transmitted by drinking contaminated water, particularly contamination by pathogens from human excreta. These include most of the enteric and diarrheal diseases caused by bacteria, parasites and viruses.Waterborne diseases also include typhoid and more than thirty species of parasites that infect the human intestines. Evidence also suggests that waterborne diseases contribute to background rates of other diseases that are not detected or explicitly reported as outbreaks.Water-washed diseases occur when there is insufficient water for washing and personal hygiene or when people wash with contaminated water. These include blindness caused by trachoma and diarrheal diseases passed from person to person.Water-based diseases come from hosts that live in water or require water during part of their life cycle. These diseases are passed to humans when the hosts are ingested or come into contact with skin.
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